Mother Nature Does It Better

The advantages and challenges of incorporating biology into the science of energy

Mohamadamin Makarem

Did you know that a houseplant is more complex in harvesting energy than any solar farm on Earth? Plants use complex machinery and multistep processes to transform light energy into chemical energy, and this is not the only process in which biological systems, like plants, perform better than human-made devices. The movement of body muscles or the highly organized formation of cellulose fibers in plants are among the many examples of processes in biological systems that are far more advanced than human-designed systems.

In addition, biological systems have abilities to self-correct, reproduce, and heal; human-made devices do not usually possess these properties. So, you may ask: if biology is doing a much better job, why not replicate the same processes for human benefits? To do this, we first need a better understanding of how biological systems work. Here, three Energy Frontier Research Centers (EFRCs) are setting their mission to expand the boundaries of science on complex biological systems and fabricating devices inspired by nature.

Unraveling complex biology

Biological systems have been modifying themselves through billions of years of evolution, and these advances produced systems with greater complexity.

For example, researchers in CLSF are trying to unravel the process of cellulose formation and growth in plant cell walls. To make their intricate cell walls, plants use various biological nano-machines to synthesize cellulose. These nano-machines work like very small factories, receiving glucose units from one side, making these units into chains, and extruding them to form crystalline cellulose fibers. The structure, assembly, and functioning of these nano-machines are still unclear and demand deeper fundamental studies to elucidate.

The complex structure of cellulose synthase is modeled by a team at CLSF to understand the arrangement of cellulose synthase on the cell wall membrane. The synthase is an enzyme on the cell membrane that catalyzes the polymerization of glucose into cellulose chains. It contains 506 amino acids. The team’s work challenges a long-held belief on how cellulose synthase is assembled on the membrane to extrude cellulose and confirms that 18 synthase enzymes are needed to form a terminal complex. Image: Sethaphong et al. (see “More Information”)

Scientists struggle to get the answers they want because of limitations in characterization technologies, as complex structures are hard to unravel at the atomic level. The sensitivity of biological systems to temperature, pressure, radiation, etc., limits the techniques that can be used to resolve the structure of proteins, enzymes, or scaffolds. Moreover, the heterogeneity and lack of regular physical order in biological structures limit the information gained from many techniques, such as electron microscopy, that are often used to study the structure of hard materials.

Researchers at CLSF find themselves on the front line to tackle these challenges, and they often invent the technology required for deepening their knowledge on a particular biological process through technological advancements in spectroscopy, microscopy, gene modification, modeling, and reconstitution of biological processes from isolated components.

Inspired by biology; made by humans

In light of the complexities in biological systems, most of the time, scientists do not try to replicate exact biological processes. Instead, they try to use the inspiration derived from these processes to invent new systems to transform energy from one form to another, like transforming thermal energy into mechanical energy or transforming photons’ energy into chemical energy.

At the Center for Bio-Inspired Energy Science (CBES), another EFRC, scientists are keeping their eyes on a variety of biological processes that are doing a better job than their human-made counterparts, and with inspiration from these systems, they are designing new devices.

“The most important product of CBES is idea generation rather than synthesizing a specific compound,” said George Schatz, a member of CBES team from Northwestern University.

Because of the diverse areas of knowledge that EFRCs bring together, ideas can be offered, challenged, refined, and tested experimentally and theoretically. This idea-oriented research has allowed CBES to design many devices with inspiration from different areas of biology, such as plants, bacteria, DNA, and numerous other systems. They have developed polymers that act like muscles, in which they demonstrate expansion and contraction by external stimulation such as heat.

(a) The conical shape ion pumps are designed with inspiration of ion pumps existing in biological systems. (b) The muscle-inspired hybrid polymer actuator is sensitive to heat. Top image is when there is no heat, and bottom image shows when heat is applied. Image: Zhang et al. for 2(a) and Chin et al. for 2(b). (See “More Information”)

Also, they’ve used inspiration from photosynthesis to create structures in which photons are harvested by nanoparticle antenna structures that accumulate enough energy for reactions that require more than one photon.

Further, they’ve taken cues from ion pumps in cell membranes to design highly efficient devices that can be used for wastewater treatment. These are just a few examples of devices inspired by biology designed at CBES because of their idea-oriented approach to research.

Being as good as plants

Utilizing an understanding of biological systems to improve design of new systems is not limited to taking inspiration from a general idea of how the biology works. Sometimes there is a need to design a specific device that performs as well as its biological counterpart. This can lead to more and more complicated designs. Consequently, the question is: How are researchers dealing with complexities in new designs?

“We are not necessarily building to the full complexity of a biological system,” said Gabriela Schlau-Cohen, assistant professor at Massachusetts Institute of Technology and member of the Bioinspired Light-Escalated Chemistry (BioLEC) team.

To implement the current understanding of biological systems into new energy-harvesting devices, researchers at the recently established BioLEC are launching new projects to put pieces from synthetic chemistry, device fabrication, characterization, and biology together to invent new ways of cultivating energy with inspiration from photosynthesis.

Plants have an advanced way of harvesting energy from sunlight using the process of photosynthesis. “Because plants have already figured out a better procedure to harvest energy, there is no need to reinvent the wheel,” said Schlau-Cohen.

Scientists observe the reaction mechanisms in place for photosynthesis and try to implement them into new designs. During photosynthesis, photons’ energy is used to induce chemical reactions. To facilitate these reactions, plants use complex structures that act as photoredox catalysts. Photoredox catalysts use energy from light photons to perform an oxidation-reduction reaction, where electron transfers between chemical species to produce new products. Human-made photoredox systems are limited to one photon reaction with low absorption cross-section, causing low turnover of these systems.

However, plants solved this problem by creating large chemical “antennas” to absorb light and funnel the light into the catalytic site, so all the needed energy arrives at a fast pace to these sites. The chemistry that is common in photosynthesis of plants is still not possible to do in a lab environment, because there is not enough detailed understanding of these mechanisms at the molecular level. Therefore, scientists at BioLEC are focusing their effort to design, fabricate, and characterize systems with higher absorption cross-sections and multi-photon excitation capabilities.

The world seen through the eyes of a biologist is very different than that seen through the eyes of chemists, physicists, and engineers. Thus, the work in CLSF, BioLEC, and CBES EFRCs is crucial to make connections between different viewpoints, so the advances in one area of science aren’t limited to its initial field. Conquering the difficulties in understanding how plants and other biological systems work and creating a strong connection between different scientific fields advances energy science, where devices inspired by nature can be used to improve not only energy systems but other industrial processes as well.

Acknowledgments

Chin et al.: This work was primarily supported by the Center for Bioinspired Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences. The 3-D printing experiments were supported by the Air Force Research Laboratory. S.M.C. and A.N.E. acknowledge graduate research fellowships through the National Science Foundation. C.V.S. acknowledges a Feodor Lynen-postdoctoral fellowship through the Humboldt Foundation. Z.A. has received postdoctoral support from the Beatriu de Pinós Fellowship 2014 (Agència de Gestió d’Ajust Universitaris i de Recerca, AGAUR), and a grant from the PVA Research Foundation. N.A.S. was supported by the Department of Defense, Air Force Office of Scientific Research, through the National Defense Science and Engineering Graduate Fellowship, 32 CFR 168a, and Northwestern University International Institute for Nanotechnology through a Ryan Fellowship. This research used resources of the Advanced Photon Source, a DOE Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory. This work used core facilities at Northwestern University.

Sethaphong et al.: L.S., J.D.K., C.H.H., and Y.G.Y. was supported as part of the Center for Lignocellulose Structure and Formation, Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Science. Work by S.D. was supported by National Science Foundation. Work by J.Z. was support by National Institutes of Health and start-up funds from the University of Virginia School of Medicine. Work by D.B. was supported by the National Science and Engineering Research Council of Canada.

Zhang and Schatz: This work was supported as part of the Center for Bioinspired Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.

About the author(s):

Mohamadamin Makarem is a Ph.D. candidate in chemical engineering at Pennsylvania State University. He is a member of the Center for Lignocellulose Structure and Formation, an Energy Frontier Research Center. His research focuses on studying the orientation and packing of cellulose microfibrils in plants using sum frequency generation vibrational spectroscopy.